In recent years, in order to enhance visibility of image display devices, a gap between an image display panel such as a liquid crystal display (LCD), a plasma display (PDP), an electroluminescence display (ELD) and a protective panel or a touch panel member disposed on the front side (viewing side) thereof has been filled with a bond to suppress reflection of incident light or light emitting from the display image at an air layer interface.
As such method for filling the gap between the image display device constituent members with an adhesive, a method is known in which a liquid adhesive resin composition containing a UV-curable resin is filled in the gap and then cured by irradiating with UV light (Patent Document 1).
In addition, a method to fill the gap between the image display device constituent members with an adhesive sheet is also known. For example, Patent Document 2 discloses a method including bonding a primary crosslinked adhesive sheet by UV light to the image display device constituent members, and thereafter irradiating the adhesive sheet by UV light via the image display device constituent members for secondary curing.
Patent Document 3 discloses a method to fill the gap between the image display device constituent members with an adhesive sheet formed from a hot-melt type adhesive composition which contains urethane (meth)acrylate having a weight average molecular weight of 20,000 to 100,000 as a main component and in which the loss tangent at 25° C. is less than 1.
Incidentally, in the image display devices such as mobile phones, mobile terminals, and the like, a concealed section is generally printed in a frame shape at the periphery of a surface protection panel. In the case of bonding the image display device constituent members with the photocurable adhesive or the adhesive sheet as described above, when the concealed section is present, there is a problem that it is difficult to obtain a stable quality since there are places where UV light irradiated to cure the adhesive hardly reaches and thus such places could not be cured.
Hence, for instance, Patent Document 4 (Japanese Patent Laid-Open No. 2013-184997) discloses a liquid photocurable resin composition containing an ethylenically unsaturated bond-containing component, a photopolymerization initiator having a maximum absorption wavelength in the range of 370 to 420 nm, and a phosphor, as the liquid photocurable resin composition which can be well cured even at the shadow part, the narrow gap part, or the like.